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Aug. 11, 1959 B. D. POWEQR 2,899,127

v VAPOUR VACUUM PUMPS Filed Dec. 10, 1956 2 Sheets-Sheet l NVENTOR Ems/70 731m: I

Aug. 11, 1959 B. D. POWER VAPOUR VACUUM PUMPS 2 Sheets-Sheet 2 Filed Dec. 10, 1956 lNvaN-rez jouv/p BY W v r ATTORNEY United States Patent VAPOUR VACUUM PUMPS Basil Dixon Power, Langley Green, Crawley, England, assignor to Edwards High Vacuum Limited, =Crawley, England, a British company Application December '10,:1956,'Serial No. 627 ,455

Claims priority, application Great Britain December 8, 1955 8 Claims. (Cl. 230-101) The present invention relates to vapour vacuum pumps. In the operation of vacuum pumping systems it is in many cases desirable, for example wherever industrial production involves a batch-vacuum process, that the system should be capable of being rapidly brought up to atmospheric pressure and rapidly re-evacuated.

If the vacuum system is being pumped by a vapour vacuum pump (e.g. a so called diffusion pump) it is undesirable that the pump boiler, while it is at working temperature, be exposed to air at atmospheric pressure thereby causing damage to "the pump working fluid and other undesirable consequences, for example, the loss and carry over of the working fluid into the rotary backing pump if re-evacuation is carried out whilst the fluid is still hot and also super heating of the fluid at atmospheric pressure it the heaters remain on during the period.

When the vapour pump is connected directly to the system being'purnped'it is therefore in-many cases necessary, when it is desired to bring the system -up to atmospheric pressure, first to interrupt the heating of theboiler of the pump and-allow the boiler to cool before admitting air to the system. When re-evacuating the system a rough" vacuum is first produced in the vapour pump and system with the fore pumping means and then the heating of the boiler .is again applied to heat the boiler again to operating temperature. It will be apparent that the boiler cooling and'heating times involved make the desirable rapid atmospheric pressure-vacuum cycles impossible.

It has therefore become common and indeed essential practice, in many vacuum pumping systems, to provide an isolation valve between the vapour-pump .and thesystem being pumped, together with a valve-controlled bypass duct from the system being pumped to a rough pumping means. When it is required to bring the pumped system up to atmospheric pressure, the isolation valve is closed and air can be admitted to the system while the vapour pump sealed oh by the isolation valve, .continues to operate at vacuum. In order to re-evacuate the system, the system .is first rough pumped through the bypass duct, and then the by-pass valve is closed and the isolation valve opened so that :the :fully operative vapour pump is again connected to the system. The above mentioned delays due tocoolingandheating vof the boiler are thusentirely avoided.

Owing to the characteristics of flow under high vacuum conditions, it is .necessary .that the isolation valve ports and apertures have an area as largeas or larger than the vapour pump moutharea in order to avoid that the valve unduly restrict the pumping speed available in the system, and as pumping systems :grow larger .and higher efiective pumping speeds become essential it is increasingly difiicult to provide suitable isolation valves. For example, an isolation valve fora ,24 inch diameter vapour pump would desirably have ,a port diameter of not less than 24", and a body and exit diameter of the order of 36". Such a valve may cost as :much or more than the vapour pump itself and apart from increasing the d-ifliculty ofmainte- 2 nance and service, considerably reduces the pumping speed.

'It is an object of this invention to provide a vacuum vapour pump which can be connected directly to the system to be evacuated, and can be operated to produce rapid exhausting cycles from atmospheric pressure to operating vacuum without dangerous exposure of the pump to atmospheric pressure.

According to the present invention, a vapour vacuum pump is provided withmeans for controlling operation thereof comprising valve means for isolating the boiler of the pump from the main duct supplying vapour to thejet or jets of the pump, and means for controlling the operation of the boiler during the time the boiler is isolated from the main duct, so that upon restoring communication of the boiler with the main duct the pump enters substantially immediately into efiective operation.

According to a further feature of the invention the said controlling means comprises condensing means for condensing vapour generated by the boiler during the time that the boiler is isolated from the main duct, i.e. the idle period of the pump, at a rate such that the temperature gradients associated with the heat flow into the boiler, and the pressure in the boiler respectively are maintained at predetermined controlled values.

In this manner it is possible to maintain the boiler pressure and the temperature gradient from the heating means through the boiler shell to the operating fluid, substantially the same as under normal operating conditions of the boiler, so that at the end of an idle period, and upon restoring communication of the boiler with the main vapour duct, the pump assumes. its full pumping capacity practically instantaneously.

It is'also possible .to permit the "boiler pressure and temperature to riseby a predetermined controlled amount during the idle period, so that upon restoring communication of the boiler with the main vapour duct the maximum mass throughput and the maximum backing pressure against which the pump will operate are temporarily increased and gradually return to normalas the pump-down proceeds.

The invention will now be described with reference to the accompanying drawings, in which:

Figure 1 illustrates diagrammatically a single stage vapour pump embodying the invention in its simplest form,

Figures 2 and 3 illustrate respectively alternative arrangements of a pump according to the invention including means for maintaining the boiler at normal operating temperature, and

Figure 4 shows in diagrammatic form a combination of the construction of Figures 1 and 2.

Referring firstly to Figure 1 there is shown a single stage pump having a casing 31 and provided with a valve 1 in the roof'of the boiler of the pump for isolating the boiler from the main duct 2 supplying vapour to the jet 3. A return pipe 4 is provided for returning condensed vapour to the boiler, and includes a valve 5 for isolating the boiler from the body of the pump. When it is desired to admit air to the system being pumped, avalve (not shown) leading to a fore pump, is closed, or the fore pump is shut down. The valves 1 and 5 are then closed so that the boiler is thus protected from the entry of air and may remain at operating temperature with safety for an indefinite period provided there is no air leakage. Alternatively, the valve 5 may be omitted and the return pipe 4 is provided with a bend to form a liquid lock, and enters the boiler above the port of the vapour line valve 1 as shown in dotted line .at 6. By this means the need for a separate return pipe valve is avoided, and the vapour line valve 1 serves to :isolate the return pipe from the boiler in addition to isolating the boiler from the main duct. There is, however, the danger with this alternative construction that a certain amount of liquid which may happen to be flowing over the heated roof of the boiler at the moment that the valve 1 closes may be damaged by exposure to air whilst hot, or may volatilize from the hot roof even under atmospheric pressure thereby causing contamination in the system. i

The liquid lock referred to above may therefore, in a further alternative arrangement take the form of a pot with a metal bellows section as shown at 8 in Fig. 2. The movement of the bellows when the internal pressure changes due to the admission of air, ensures that the pot capacity is increased at this time providing a storage space for any pump liquid remaining above the vapourline valve In when this is closed. The construction is such that liquid remaining on the roof of the boiler can drain back either directly into the pot 8 or after voltalization and condensation in the pump body.

In the above described arrangements, when the vapour valve 1 or 1a is closed, no more vapour is discharged from the boiler and if the heaters are left operating the boiler pressure and temperature will rise continuously, so that after a time a dangerous condition will result. If on the other hand the system is re-evacuated and the vapour-line valve re-opened before the dangerous condition is reached the consequences are still likely to be undesirable since when the overheated liquid in the boiler is suddenly exposed to a pressure far less than its normal boiling pressure at the temperature reached, a period of extremely violent boiling ensues and liquid may spit and froth from the jets and out of the pump thereby producing severe contamination of the system and loss of fluid to the fore pump.

An arrangement whereby the boiler is maintained in normal operating condition during the time that it is isolated from the main vapour duct, is shown in Fig. 2.

In the construction of Fig. 2 in addition to a line valve 1a, liquid return pipe 4a, and liquid lock 8, there is provided an additional vapour outlet in the roof of the boiler in the form of an orifice plate 7 adapted to be closed by a valve 9. The said additional outlet communicates with a condenser 10 and a return duct 11 for condensed pumping fluid leads from the condenser into the boiler and includes some form of liquid lock. The orifice in the orifice plate may be so made and dimen sioned that it offers resistance to vapour flow equivalent to the total resistance offered by the vapour jet (or vapour jets in the case of a multi stage pump) and duct or ducts leading thereto.

It will be apparent that when the vapour line valve 1a is closed so that atmospheric pressure can be admitted above it, and the valve 9 is opened, a path for vapour from the boiler is provided having (in the general case) a resistance for vapour flow equivalent to that of the normal vapour path from the boiler, and leading to an effective condenser.

Vapour flow from the boiler thus continues when the valve 1a is closed at the same rate as under normal operating conditions of the boiler, and condensate is returned to the boiler through the duct 11. The boiler heaters can be left delivering the same power and the boiler pressure and thermal gradients through the base of the boiler will remain substantially the same as for normal operation, the boiler thus being kept ready for instant re-use.

Vapour pumps generally pump fastest in the higher pressure range when provided with a comparatively high boiler pressure, but pump fastest in the lower pressure range with a reduced boiler pressure. It is thus an advantage to begin the evacuation of a system with a high heater input to the pump and to reduce the heater input as evacuation proceeds to a lower pressure region.

In the construction of Fig. 2, if the orifice of the orifice plate 7 is made of a size so as to provide somewhat more resistance than the normal vapour path from the boiler, the boiler temperature and pressure will rise by an automatically controlled amount during the idle period of the boiler so that by supplying the boiler with a fairly moderate heater input during the idle period, the temperature and pressure are caused to rise to a value corresponding to a greater heater input. The thermal capacity of a large boiler can be such that this higher boiler pressure can be effective during the early or high pressure part of the pump-down, the boiler pressure and temperature returning progressively to normal as the pump-down proceeds. In other words, the heat extracting means shown as a condenser 10 connected to the vapor space of the boiler, and provided with means shown as valve 79 selectively operable for rendering said heat extracting means 10 effective to extract heat from the boiler while the isolating valve means la is closed, may have a capacity to extract heat, at a normal operating temperature and pressure of the boiler, which is substantially equal to, or somewhat smaller than, or even somewhat greater than the normal rate of supply of heat to the boiler by its heater, but which at least approaches said normal rate so that ineffective and dangerous conditions are eliminated, and so that the pump may substantially immediately enter into fully effective operation when pumping operation of the pump is established or reestablished.

A boiler of the construction shown in Fig. 2 can thus remain safely in operating condition for an indefinite period with the vapour-line valve 1a closed, provided there is no ingress of air. Any considerable leakage or ingress of air or gas would cause the pressure in the boiler to rise dangerously. It is advisable, therefore, particularly if idle periods are likely to be fairly long, to arrange valves for controlling the piping to the backing pump of the vapour pump, so that the backing pump can maintain a low air pressure in the boiler during idle periods. Alternatively, and particularly when rough pumping of the system takes a long time so that the boiler would have to be left unpumped for a considerable period during roughing, a small holding pump as shown in dotted line at 12 in Fig. 2 may be provided.

In the further alternative construction of Fig. 3 the valve 9 and condenser 10 of Fig. 2 are replaced by a water cooled finger 13 and water valve 14. The surface of the finger 13 is just sutficiently large to condense vapour at a rate corresponding to the normal vapour load on the boiler when the pump is in normal operation, and is thermally insulated from the main boiler wall by a low conductivity sleeve (not shown).

When the pump mouth is to be exposed to atmospheric pressure, the valve 1a is closed and the water valve 14 is opened. The conditions in the boiler (boiler pressure, temperature gradients, etc.) then remain normal indefinitely.

When the pump is brought into use again the water valve 14 is closed and the valve 1a opened. The cooled finger 13 then drains instantly through a drain duct 15 and quickly heats to boiler temperature, the casing forming the finger being of small thermal capacity.

The finger 13 can of course be replaced by any other suitable form of cooled surface of defined area, such as for example a water tube extending across the lower part of the boiler in the path of the vapour. The tube slopes slightly downwardly and is connected at its higher end through a suitable valve to a cold water supply, the lower end of the tube discharging into a drain.

Referring now to Fig. 4 of the drawings, there is shown a pump which combines features of the boilers of Figs. 1 and 2. Thus the pump of Fig. 4 comprises a boiler 16 from the roof of which a vertical duct 17 leads to a transverse duct 18 from one end of which extends a main duct 19 for supplying vapour to the jet 20 of the pump. The condensate from the jet 20 is fed back to the boiler 16 through a pipe 21, and control valve 22.

aeeara'? 3 The other end of the transverse duct 18 is provided with cooling means 23 and a pipe 24 leads from the said other end to the boiler for returning condensed vapour from the duct 18 to the boiler.

Adjacent the main duct 19, the transverse duct is provided with an orifice 25 adapted to be closed by a valve member 26 for interrupting the supply of vapour to the main duct, the valve member 26 thus corresponding to the valve 1a of Fig. 2. Also positioned in the transverse duct 18, between the vertical duct 17 and the cooled end of the transverse duct, there is an apertured plate 27 the apertures of which are adapted to be closed by a valve plate member 28, corresponding to the valve 9 of Fig. 2.

The valve member 26 and the valve plate member 28 are secured to a common spindle 2.9 slidably supported in the transverse duct 18 and operable by means of a handle 3i), the arrangement being such that when the spindle 29 is moved in one direction the valve member 26 opens the orifice 25 and the valve plate member 28 closes the apertures of the plate 27, and when the spindle is moved in the other direction, the valve member 26 closes the orifice 25 and the valve plate member 28 uncovers the apertures of the plate 27.

The operation of the pump shown in Fig. 4 will be readily understood from the previously described operation of the pumps of Figs. 1 and 2.

It will be understood that the invention may be applied to pumps other than that shown in the drawings, for example vapour pumps with simple or multiple and complex jet systems.

I claim:

1. In combination, a vapor vacuum pump with means for controlling operation thereof; said pump comprising a boiler having a vapor space therein, a casing having a cooled wall surface with pump inlet and outlet means spaced lengthwise thereof, vapor jet means positioned to discharge into said casing intermediate said inlet and outlet means and toward said cooled surface and said outlet means, vapor duct means leading from said vapor space to said jet means for supplying vapor to said jet means for discharge thereby to eifect pumping operation from said inlet means to said outlet means, and a heater for supplynig heat to said boiler at a normal rate effective for maintaining a normal operating pressure and temperature in said boiler during such pumping operation; said means for controlling operation of the pump comprising isolating valve means in said vapor duct means, and heat extracting means connected with said boiler, said isolating valve means being openable to permit flow of vapor to said jet means for establishing pumping operation of the pump and being closable to suspend such flow of vapor for suspending pumping operation of the pump, and said heat extracting means having a capacity to extract heat from the boiler at a rate at least approaching said normal rate of supply of heat to said boiler by said heater, and means connected with said heat extracting means selectively operable for rendering said heat extracting means effective to extract heat from said boiler at said rate while said isolating valve means is closed and for rendering said heat extracting means ineffective to extract heat from said boiler while said isolating valve means is open;

whereby a temperature gradient of heat flow from said heater to said boiler, and an operating pressure in the boiler, may be maintained while pumping operation of the pump is suspended, such that the pump may substantially immediately enter into fully effective operation when said isolating valve means is opened, and said heat extracting means is rendered ineffective, to establish pumping operation of the pump.

2. The combination of claim 1, further comprising means interconnecting said isolating valve means and said selectively operable means for rendering said heat extracting means effective when said isolating valve means is closed and for rendering said heat extracting means inefllective when said isolating valve means is opened.

3. The combination of claim 1, said heat extracting means comprising a cooling surface within said boiler, and said selectively operable means controlling cooling of said surface.

4. The combination of claim 1, said heat extracting means comprising a condensing surface within the vapor space of said boiler and said selectively operable means controlling cooling of said condensing surface.

5. The combination of claim 1, said heat extracting means connected with said boiler comprising a condenser having a vapor connection to said boiler, and said selectively operable means comprising openable cut-01f valve means in said vapor connection.

6. The combination of claim 1, said heat extracting means connected with said boiler having a capacity to draw heat from said boiler, at said normal operating temperature and pressure of said boiler, at a rate equal to said normal rate of supply of heat to said boiler by said heater, and thus being effective for maintaining said temperature gradient and boiler pressure at their normal operating value during suspension of said pumping operation of said pump.

7. The combination of claim 1, said heat extracting means connected with said boiler having a capacity to draw heat from said boiler, at said normal operating temperature and pressure of said boiler, at a rate which is less by a predetermined amount than said normal rate of supply of heat to said boiler, by said heater and thus being effective for causing the boiler temperature and pressure to increase toward a corresponding predetermined limit above their normal operating values during suspension of said pumping operation of said pump.

8. The combination of claim 1, said heat extracting means connected with said boiler having a capacity to draw heat from said boiler, at said normal operating temperature and pressure of said boiler, at a rate which is greater by a predetermined amount than said normal rate of supply of heat to said boiler by said heater, and thus being effective for causing the boiler temperature and pressure to decrease toward a corresponding predetermined limit below their normal operating values during suspension of said pumping operation of said pump.

No references cited. 

